xref: /linux/include/linux/hung_task.h (revision 7d4e49a77d9930c69751b9192448fda6ff9100f1) 
1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /*
3  * Detect Hung Task: detecting tasks stuck in D state
4  *
5  * Copyright (C) 2025 Tongcheng Travel (www.ly.com)
6  * Author: Lance Yang <mingzhe.yang@ly.com>
7  */
8 #ifndef __LINUX_HUNG_TASK_H
9 #define __LINUX_HUNG_TASK_H
10 
11 #include <linux/bug.h>
12 #include <linux/sched.h>
13 #include <linux/compiler.h>
14 
15 /*
16  * @blocker: Combines lock address and blocking type.
17  *
18  * Since lock pointers are at least 4-byte aligned(32-bit) or 8-byte
19  * aligned(64-bit). This leaves the 2 least bits (LSBs) of the pointer
20  * always zero. So we can use these bits to encode the specific blocking
21  * type.
22  *
23  * Type encoding:
24  * 00 - Blocked on mutex        (BLOCKER_TYPE_MUTEX)
25  * 01 - Blocked on semaphore    (BLOCKER_TYPE_SEM)
26  * 10 - Blocked on rt-mutex     (BLOCKER_TYPE_RTMUTEX)
27  * 11 - Blocked on rw-semaphore (BLOCKER_TYPE_RWSEM)
28  */
29 #define BLOCKER_TYPE_MUTEX      0x00UL
30 #define BLOCKER_TYPE_SEM        0x01UL
31 #define BLOCKER_TYPE_RTMUTEX    0x02UL
32 #define BLOCKER_TYPE_RWSEM      0x03UL
33 
34 #define BLOCKER_TYPE_MASK       0x03UL
35 
36 #ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER
hung_task_set_blocker(void * lock,unsigned long type)37 static inline void hung_task_set_blocker(void *lock, unsigned long type)
38 {
39 	unsigned long lock_ptr = (unsigned long)lock;
40 
41 	WARN_ON_ONCE(!lock_ptr);
42 	WARN_ON_ONCE(READ_ONCE(current->blocker));
43 
44 	/*
45 	 * If the lock pointer matches the BLOCKER_TYPE_MASK, return
46 	 * without writing anything.
47 	 */
48 	if (WARN_ON_ONCE(lock_ptr & BLOCKER_TYPE_MASK))
49 		return;
50 
51 	WRITE_ONCE(current->blocker, lock_ptr | type);
52 }
53 
hung_task_clear_blocker(void)54 static inline void hung_task_clear_blocker(void)
55 {
56 	WARN_ON_ONCE(!READ_ONCE(current->blocker));
57 
58 	WRITE_ONCE(current->blocker, 0UL);
59 }
60 
61 /*
62  * hung_task_get_blocker_type - Extracts blocker type from encoded blocker
63  * address.
64  *
65  * @blocker: Blocker pointer with encoded type (via LSB bits)
66  *
67  * Returns: BLOCKER_TYPE_MUTEX, BLOCKER_TYPE_SEM, etc.
68  */
hung_task_get_blocker_type(unsigned long blocker)69 static inline unsigned long hung_task_get_blocker_type(unsigned long blocker)
70 {
71 	WARN_ON_ONCE(!blocker);
72 
73 	return blocker & BLOCKER_TYPE_MASK;
74 }
75 
hung_task_blocker_to_lock(unsigned long blocker)76 static inline void *hung_task_blocker_to_lock(unsigned long blocker)
77 {
78 	WARN_ON_ONCE(!blocker);
79 
80 	return (void *)(blocker & ~BLOCKER_TYPE_MASK);
81 }
82 #else
hung_task_set_blocker(void * lock,unsigned long type)83 static inline void hung_task_set_blocker(void *lock, unsigned long type)
84 {
85 }
hung_task_clear_blocker(void)86 static inline void hung_task_clear_blocker(void)
87 {
88 }
hung_task_get_blocker_type(unsigned long blocker)89 static inline unsigned long hung_task_get_blocker_type(unsigned long blocker)
90 {
91 	return 0UL;
92 }
hung_task_blocker_to_lock(unsigned long blocker)93 static inline void *hung_task_blocker_to_lock(unsigned long blocker)
94 {
95 	return NULL;
96 }
97 #endif
98 
99 #endif /* __LINUX_HUNG_TASK_H */
100